First you would need to be able to download your autosomal raw data from your testing service. It should save to a text or csv (comma delimited file). If they provide the raw data, it should be a large file containing hundreds of thousands of lines. Each line should contain fields for the RSID, Chromosome, Position and the Value. If your service does not allow you access to your raw data, or if your raw data does not contain those fields, then you are out of luck.
Next you would have to convert your raw data to the format of one of the companies that MyHeritage DNA can import, i.e., Ancestry DNA, Family Tree DNA, or 23andMe.
If I were trying to do this, I would load the raw data into Excel, change it to the raw data format of, say, Family Tree DNA, and then save it from Excel as a csv file. The Family Tree DNA raw data looks like this:
where the first line is a header line and the next 3 show how the rest of them would look.
I would give the file a name similar to one those of Family Tree DNA raw data files, e.g. 37_Testers_Name_Autoso_20170621.csv, and then try uploading it. Maybe MyHeritage would take it or maybe it would not. It would depend on what checks MyHeritage does to ensure it is a Family Tree DNA raw data file.
Even if MyHeritage DNA takes it, you might or might not get very good results, depending on what RSIDs your testing company include in their raw data file and whether these overlap enough with the RSIDs that MyHeritage tests for. MyHeritage does imputation for RSIDs that are missing and that will cause some inaccuracy.